Unmanned Aerial Vehicles (UAVs) have enormous potentials for several important applications, such as search and rescue and structural health monitoring. An important requirement for these applications is the ability to accurately localize objects, such as sensors or ''smart-things'', equipped with wireless communication capability. However, most previous works in this area neglect the unavoidable errors that are involved in the localization process, thus resulting in poor performance in practice. In this paper, for the first time, we express the measurement error on the ground as a function of the rolling, altitude, and instrumental precision provided by the hardware on the drone. We takeaway two lessons from this analysis: to limit the ground error (i) all the waypoints used to measure the same node must be at a sufficiently large ground distance from the node itself, and (ii) they must not be collinear among themselves nor with the node. We validate the error expressions derived analytically through real experiments using the 3DR Solo Drone.